There has been provided various types of sky wave receiving antennas such as dipole, pole, loop, parabola, Yagi and log periodic antennas, among which the log periodic antenna is much broadly used in the receiving antenna field. The log periodic antenna includes a horizontal support rod, a radiator placed across the support rod and a plurality of constantly spaced directors placed in parallel, and is horizontally installed to receive sky waves with the aid of structures like pipes or walls through clamping devices.
For the receiving antenna, it is necessarily required to adjust a receive angle of the antenna for receiving signals with directivity from a particular direction. The adjustment structure for adjusting the receive angle of the receiving antenna is accomplished with the use of the clamping devices by turning in a right or left direction with keeping the receiving antenna stable in its horizontal direction.
The angular adjustment of the receiving antenna for reception of signals only in a horizontal direction results in low reception ratio due to failure of the adjustment of the receiving antenna in the scanning direction for signals from the transmitting station, i.e., failure of the adjustment in the vertical direction of the receiving antenna.